Reduction of energy consumption of vapour compression systems, such as refrigeration systems, air condition systems or heat pumps, is desired. Various efforts have been made to improve the components of vapour compression systems to reduce the energy consumption of the individual components, and of the vapour compression systems as such.
Furthermore, the expansion valve of a vapour compression system may advantageously be operable to control the amount of refrigerant being supplied to the evaporator to utilise the available cooling or heating capacity of the vapour compression system to the greatest possible extent.
U.S. Pat. No. 5,002,089 discloses a variable area refrigerant expansion device for heating mode of a heat pump. The expansion device comprises an elongated member extending into a metering port. The elongated member and the metering port cooperate to define a flow metering passage between the elongated member and the metering port. The elongated member is configured to vary the cross-sectional area of the flow metering passage in relation to the position of the elongated member to the metering port. A spring is mounted in a bellows which is connected to atmospheric pressure. The spring and the atmospheric pressure acting on the bellows in combination push the elongated member in a first direction. When the system is shut off a positive pressure inside the system results in a force acting on the bellows which exceeds the combined force exerted on the bellows by the spring and atmospheric pressure. As a result, this force causes the elongated member to be biased in a second direction, opposite to the first direction, and moving an enlarged head of the elongated member into sealing engagement with a boss. The positive pressure must be sufficiently high to overcome the force exerted on the bellows by the spring and the atmospheric pressure.
FR 2 661 977 discloses an expansion device comprising a movable piston comprising a metering port. The piston is movable inside a housing relative to an elongated member which is fixed relative to the housing, and which has a conical shape. Thereby the metering port and the elongated member cooperate to define a metering passage. A stop element is mounted on an end part of the elongated member. A spring is mounted inside the housing and forces the movable piston in a direction towards the stop element. A seal is required between the movable piston and the inner wall of the housing in order to provide a tight valve. This has the consequence that a certain minimum force must be applied to initiate movements of the piston, in order to overcome the friction force between the piston and the wall of the housing. Thereby it is difficult to move the piston in a precise manner, and it is not possible to adjust the flow through the valve in a precise manner.
U.S. Pat. No. 5,052,192, U.S. Pat. No. 5,038,579 and U.S. Pat. No. 4,341,090 all disclose expansion valves in which one or two piston(s) is/are mounted movably inside a housing, and relative to an elongated member, which is fixedly mounted inside the housing, similar to the valve disclosed in FR 2 661 977.